Prognostic values of blood pH and lactate levels in patients resuscitated from out-of-hospital cardiac arrest

Aim: Early prediction of prognosis after out-of-hospital cardiac arrest (OHCA) remains difficult. High blood lactate or low pH levels may be associated with poor prognosis in OHCA patients, but these associations remain controversial. We compared blood lactate and pH levels in OHCA patients transferred to our hospital to measure their prognostic performance.

Methods: We investigated the associations between blood lactate and pH levels on admission and neurological outcomes in 372 OHCA patients who had a return of spontaneous circulation.

Results: Of the 372 OHCA patients, 31 had a favorable neurological outcome. Blood lactate levels were lower in patients with a favorable outcome than in those with an unfavorable outcome, but this difference did not reach statistical significance (82 ± 49 vs. 96 ± 41 mg/dL). However, pH levels were significantly higher in patients with a favorable outcome than in those with an unfavorable outcome (7.26 ± 0.16 vs. 6.93 ± 0.19, P < 0.001). The relative cumulative frequency distribution curve analysis showed the optimal cut-off points of lactate and pH to be approximately 80 mg/dL and 7.05, respectively. Sensitivity and specificity to predict a favorable outcome were 61% and 64% for lactate <80 mg/dL and 84% and 80% for pH >7.05, respectively. Areas under receiver-operating characteristic curves were significantly larger for pH than for lactate levels (P < 0.001). In multivariate analysis, pH >7.05 was an independent predictor for a favorable outcome.

Conclusion: After OHCA, patients with a favorable outcome had lower lactate and higher pH levels than those with an unfavorable outcome, but pH level was a much better predictor for neurological outcome than lactate levels.